For new good cells, the drop is even below 1%/year from my tests.
Used cells can drop faster.
I consider acceptable the ones that were charged at 4.2 V and did not drop below 4.0 V after 1 year.
Note that the drop level depends a lot also on the type of the cell.
Many of even the used ones I have maintained 4.1-4.15 V after 1 year.
There is a direct link between V-drop over time and the general cell integrity. The ones dropping under 4.0 V (3.6-4) after 1 year I found to be very low capacity when tested, the ones ending up at around 3.3 even lower and the ones dropping below 3 were of 100-200mAh capacity.